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Why is Japanese knotweed a problem?

Japanese knotweed (Fallopia japonica) appears differently throughout each of the four seasons, meaning it can be a constant thorn in a homeowner’s side.

The plant is a non-native species to the UK. Without the natural brake on its spread, found in its native environment, it has taken on an invasive nature. As well as upsetting the UK’s ecosystem, mature plants can undermine man-made structures; damage has been recorded in buildings, hard-standing walls and drains.

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Japanese knotweed is therefore governed by legislation and is a recognised risk to property. In recent years, this has seen mortgage lenders refuse to lend on property at risk from knotweed and required developers to bring in specialists to eradicate the plants on infected sites.

The presence of knotweed on or near your property could therefore present you with a problem.

Who to turn to

We have produced an information paper to help homeowners, purchasers and lenders make informed decisions; this sets out a framework for objectively assessing and reporting the risk.

Where a known or suspected presence of knotweed is highlighted on a TA6 Property Information Form or by a buildings survey, a Specialist Knotweed Survey should be carried out to establish the risk and advice on a remediation solution.

Most UK mortgage lenders will want to see evidence of a commitment by the owner of the property to fund, in advance, a long-term chemical treatment programme against Japanese knotweed, or provide instant eradication by way of excavation and removal — this is often referred to as a knotweed management plan.

Chemical treatment can take approximately two to three years to provide effective control of the knotweed; however, it is important to note that this does not remove the rhizome (root) from the ground, which can remain dormant for many years. Where the restriction of ground-under-treatment is undesirable, or where there are known plans to disturb the ground, the excavation and removal of knotweed is often preferred.

If you can negotiate an instant removal of knotweed by excavation, do so.

How are you protected?

A guarantee is often required on any remedial works, with durations of 5–10 years being the norm. A guarantee should ensure that, should there be any recurrence of knotweed growth (as a defect of the remedial works undertaken), it will be treated and controlled at no additional expense to the property owner.

Because treatment programmes can stretch over many years, mortgage lenders will often look for an insurance backed guarantee (IBG) product, such as that provided by PCA IWCG members. This ensures that in the event a knotweed contractor providing a guarantee goes out of business before the end of the cover period, the customer will be protected by either another PCA registered company stepping in to take on the liability, or a refund of the monetary sum left on the contract. This depends on the terms of your agreement and varies per provider.

After being put on notice, companies can be fined up to £20,000 and individuals up to £2,500, if a lack of action has a detrimental effect on the quality of life of those nearby and is considered to be unreasonable.

Japanese knotweed is not cited under any legislation that requires its presence to be notified to either the Department for Environment, Food and Rural Affairs or local planning authorities; nor is it listed under The Weeds Act 1959.

The spread of Japanese knotweed is, however, governed under the Wildlife and Countryside Act 1981, which makes it an offence to cause it to grow in the wild, and can be construed as an offence to knowingly allow knotweed to spread from your property.

On development sites, Japanese knotweed needs to be managed and handled responsibly. Any works conducted to control or eradicate the plant should be completed in reference to the Environment Agency and PCA codes of practice for the management of Japanese knotweed.